Many rendering systems, such as printers, copying machines, and fax machines, are designed to apply markings on sheet media, such as paper. The sheet media typically are held in a supply bin or a removable paper tray or cassette. Sheet media must be loaded into the supply bin or paper tray of a rendering system when the supply of sheet media has run out.
Currently available rendering systems typically include sensors that trigger a notification signal when the supply bin or paper tray is empty. Many of these types of systems, however, are incapable of determining the number of sheets remaining in the supply bin or paper tray. As a result, users of these systems are unable to determine whether there is a sufficient amount of sheet media in the rendering system to complete a rendering job.
Several potential solutions that attempt to address this problem have been proposed. These solutions typically involve measuring the height of the stack of sheet media in the supply bin or paper tray and inferring the number of sheets remaining from the measured stack height. In particular, the number of sheets remaining is estimated by dividing the measured stack height by an estimate of the thickness of the individual sheets. The sheet thickness may be a predetermined value or it may be inferred from the reduction in the measured stack height after each sheet is fed into the rendering system.
The accuracy of such inferential sheet counting methods, however, may be quite low, especially when the supply bin or paper tray may have been loaded inadvertently with sheets having different thicknesses. In addition, such methods cannot detect the presence of different types of sheets having different thickness before the sheets have been fed into the rendering system. As a result, these methods cannot warn users when different types of sheets are about to be used for a rendering job.
What are needed are improved systems and methods of detecting and monitoring sheet media in rendering systems that are capable of accurately counting the number of sheets and determining when sheets of different thickness are about to be used for a rendering job.